Nearly three decades later, the credit card—along with a raft of other perks—accounted for $8 billion, or about 10%, of Delta’s revenue in 2025. According to Delta CEO Ed Bastian, the co-branded credit card’s spending nears 1% of U.S. GDP annually—a figure that reflects the sheer volume of transactions flowing through the partnership across millions of cardholders.

“As Delta’s brand started to move and people started to see it as a premium brand, as a differentiated experience, Amex was critical to that because we see Amex as the premium credit card in the business,” Bastian told Fortune editor-in-chief Alyson Shontell on the latest episode of Fortune’s Titans and Disruptors of Industry podcast.

But the relationship wasn’t always so seamless.

From friction to friendship

For years, Delta and Amex struggled with a fundamental question: Whose customer was it?

“We would have difficulties with Amex because we could never figure out whose customer it was,” Bastian said. “Amex thought it was their customer because they had the credit card. Delta thought it was our customer because we’re providing the experience.”

The tension came to a head about a decade ago, when Delta sat down with Amex CEO Stephen Squeri to resolve the matter. Bastian recalled what Squeri—whom he now considers a close friend—told him: “It’s our customers. And let’s stop fighting about who’s getting what size slice, and figure out, how do we make the pie bigger?”

That reframe changed the trajectory of the deal.

“Those are the most successful relationships,” Bastian said. “It’s not when one brand is taking advantage of another or feeding off another. [It’s] when both brands legitimately raise up.”

A partnership forged in turbulence

The co-branded card’s importance to Delta came into sharper focus during one of the airline’s darkest chapters. After a post-9/11 slump battered the carrier, Bastian—then the CFO—pushed the company to file for bankruptcy in 2005. Delta emerged from Chapter 11 in 2007, and the following year, Amex delivered a $1 billion boost, marking the beginning of what would become one of the most lucrative partnerships in the aviation industry.

Now the most profitable airline in the U.S., Delta has leaned heavily into premiumization, recognizing that targeting wealthier customers would yield more revenue per seat. Flying used to be seen as a commodity, with 80% of Delta customers preferring whichever airline provided the cheapest or fastest experience, Bastian said. Rebranding as a customer-first company that rewarded brand loyalty helped transform the company.  

“If you ask people why they choose Delta, 80% would say, ‘Because it’s Delta, because the experience, the brand, the confidence I have in that company—that’s my airline,’” Bastian said.

The card pivot

Delta and Amex aren’t the only ones betting big on co-branded loyalty. American Airlines reported $6.2 billion in cash payments from co-brand and partner agreements with Citi in 2025, while Alaska Airlines saw 16% of its total revenue flow from loyalty spending. United’s deepening relationship with Chase, and Capital One’s aggressive push into premium travel cards have further raised the stakes. 

Amex, for its part, has been expanding the perks ecosystem beyond travel. CEO Squeri told Fortune in September 2025 that the company is doubling down on “lifestyle” areas—wellness, shopping, fine dining—in addition to its core travel benefits. Recent upgrades include tripling the annual hotel credit from $200 to $600 for stays booked through American Express Travel, plus early check-in, late checkout, and credits for food or spa services at more than 3,100 partner hotels.

“We have the largest array of any card company, and it keeps growing,” Squeri said.

Today, Delta is Amex’s largest card distributor. The Delta card accounts for 10% of Amex’s worldwide billings, and Delta cardholders represent 30% of Amex’s U.S. consumer spend, according to Bastian.

And the growth isn’t slowing.

“Even though we’re the largest distribution outlet, we’re growing faster than any of the other distribution outlets they have at a double-digit clip still today,” Bastian said. “That’s making the pie bigger.”